Try an infant (human) vitamin (available in the baby section at Walmart) called Poly Vi Sol **WITHOUT** iron (that part is very important!). Put a couple drops... not a droppers full- just a drip or two in one boiled egg yolk. Smash it up and feed it to her as often as she’ll eat it. She (he I don’t know, lol) probably won’t eat an entire yolk at a time for a while, so just cover refrigerate the leftovers (plastic baggie works great to keep it moist). You can add a couple drops of water to it if it gets too dried out.
I had a little English bantam chick with the same issues, she couldn’t balance, kept falling over (I read that lacking vitamin E is often the culprit there) but she also had pasty butt which is a whole other issue. After much research this is what I came up with for her (along with unsticking her vent a couple times a day) and it worked great. Took about 2 weeks of pampering for her to fully recover, but soon (before she was all the way normal) she was up running around with the rest of the chicks healthy as can be. Worth a shot! Cheap and easy.. just takes a little time.